In the past, various methods have been suggested to recover coal in situ by slurrying the coal. Some of these techniques are taught in the following U.S. Pat. Nos. 1,532,826, 3,260,548, 3,359,037 and 4,032,193. U.S. Pat. No. 4,032,193 discloses a process for treating coal in-situ with a basic aqueous solution, preferably sodium hydroxide, to disintegrate the coal. The patent states that either mechanical enlargement of the wellbore in the vicinity of alkali injection or removal of some of the initially disaggregated coal is necessary to provide adequate porosity. The patent also suggests that the coal may be contacted with a reactive oxygen-containing substance, however, it is specifically stated in column 4, lines 25 to 31, that the rate of disintegration appears to be decreased by the injection of oxygen-containing substances. Further, that patent suggests pumping nitrogen into the formation with the aqueous solution only for the purpose of providing an inert environment. There is still need, however, for a process of slurrying coal in-situ which minimizes need for mechanical operations down the well.
This application is a continuation-in-part of copending application for "Method of Recovering Coal in Aqueous Slurry Form," Ser. No. 831,035, filed Sept. 6, 1977. In that application there is disclosed and claimed a method for in situ recovery of lignitic, sub-bituminous and bituminous coal in slurry form wherein the coal is first contacted with a gaseous mixture of an oxygen-containing gas and vaporized NO.sub.2 to cause disintegration of the coal, then the coal is contacted with an aqueous caustic solution to produce a slurry and the slurried coal is removed from the formation to the earth's surface for surface processing. In that application the aqueous caustic solution is further characterized as an aqueous alkaline solution containing 0.5% to 5.0% by weight NH.sub.3 and further described as possibly containing 0.01% to 0.2% by weight of NaOH or from about 0.014% to 0.28% by weight of KOH.
In the present invention a further characterization of the aqueous alkaline solution is disclosed comprising a solution containing ethanolamine.